Another substance, called substance P, is also released from the lining of the stomach and intestines with damage by chemotherapy, and is released together with serotonin. The substance P binds to another protein called "neurokinin-1 receptor" or NK-1 receptor. These proteins are found in the intestines and another portion of the brain called "tractus solitarius". The brain then signals the body to produce nausea and vomiting.